This invention relates to an improvement of a signal band compression method, which aims at decreasing the quantity of information required in telegraph or facsimile transmission or recording, by reducing the redundancy of image information.
In facsimile, etc., a black and white character-picture indicating plane is scanned and the scanned output is binary coded. Since the resultant series of picture signals has a redundancy, it can not be accepted as an efficient method to transmit it in its original form. So, various band compression methods are nowadays proposed to eliminate a redundant part out of the binary-coded picture image information. In spite of considerable effects, a sufficient reproduction characteristic has not yet been obtained.
An adaptive prediction method is one of the prior art band compression methods. This method comprises a preliminary process in which the information value of a selected picture element is predicted by using peripheral picture elements thereof and converting their information into a signal expressing the predicted result, and comprises a means for coding this converted signal to telegraph-transmit or to record it. In such a method, the compression ratio is much dependent on the preliminary process.